Open Question
Thinking creatively about evolutionary mechanisms, identify at least two schemes that could generate allelic polymorphism in a population. Do not include the processes described in the answer to Problem 4.
21. Population Genetics
Allelic Frequency Changes
Back21. Population Genetics
Allelic Frequency Changes
- Open QuestionGenetic drift, an evolutionary process affecting all populations, can have a significant effect in small populations, even though its effect is negligible in large populations. Explain why this is the case.
- Open QuestionOver the course of many generations in a small population, what effect does random genetic drift have on allele frequencies?
- Open QuestionCatastrophic events such as loss of habitat, famine, or overhunting can push species to the brink of extinction and result in a genetic bottleneck. What happens to allele frequencies in a species that experiences a near-extinction event, and what is expected to happen to allele frequencies if the species recovers from near extinction?
- Open QuestionGeorge Udny Yule was wrong in suggesting that an autosomal dominant trait like brachydactyly will increase in frequency in populations. Explain why Yule was incorrect.
- Open Question
If 4 percent of a population in equilibrium expresses a recessive trait, what is the probability that the offspring of two individuals who do not express the trait will express it?
- Open Question
Under what circumstances might a lethal dominant allele persist in a population?
- Open QuestionTwo populations of deer, one of them large and living in a mainland forest and the other small and inhabiting a forest on an island, regularly exchange members that migrate across a land bridge that connects the island to the mainland.An earthquake destroys the bridge between the island and the mainland, making migration impossible for the deer. What do you expect will happen to allele frequencies in the two populations over the following 10 generations?
- Open QuestionTwo populations of deer, one of them large and living in a mainland forest and the other small and inhabiting a forest on an island, regularly exchange members that migrate across a land bridge that connects the island to the mainland.If you compared the allele frequencies in the two populations, what would you expect to find?
- Open QuestionTwo populations of deer, one of them large and living in a mainland forest and the other small and inhabiting a forest on an island, regularly exchange members that migrate across a land bridge that connects the island to the mainland.In which population do you expect to see the greatest allele frequency change? Why?
- Open QuestionDirectional selection presents an apparent paradox. By favoring one allele and disfavoring others, directional selection can lead to fixation (a frequency of 1.0) of the favored allele, after which there is no genetic variation at the locus, and its evolution stops. Explain why directional selection no longer operates in populations after the favored allele reaches fixation.
- Open Question
One of the first Mendelian traits identified in humans was a dominant condition known as brachydactyly. This gene causes an abnormal shortening of the fingers or toes (or both). At the time, some researchers thought that the dominant trait would spread until 75 percent of the population would be affected (because the phenotypic ratio of dominant to recessive is 3 : 1). Show that the reasoning was incorrect.
- Open QuestionWhat is inbreeding depression? Why is inbreeding depression a serious concern for animal biologists involved in species-conservation breeding programs?
- Open QuestionCertain animal species, such as the black-footed ferret, are nearly extinct and currently exist only in captive populations. Other species, such as the panda, are also threatened but exist in the wild thanks to intensive captive breeding programs. What strategies would you suggest in the case of black-footed ferrets and in the case of pandas to monitor and minimize inbreeding depression?
- Open Question
Achondroplasia is a dominant trait that causes a characteristic form of dwarfism. In a survey of 50,000 births, five infants with achondroplasia were identified. Three of the affected infants had affected parents, while two had normal parents. Calculate the mutation rate for achondroplasia and express the rate as the number of mutant genes per given number of gametes.